Internal angular dermoid cyst
Swelling since birth adjacent to the medial canthus of the left orbit with slow increase in size over the years.
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A left-sided superficially located space occupying lesion is noted involving the medial aspect of the preseptal region of the left upper eyelid extending to the region of the inner canthus. It is still separable from the region of the left lacrimal sac. It flattens against the maxillary process of the left frontal bone and the proximal aspect of the left nasal bone. No intra-orbital or intra-cranial extension could be seen. It showed non-enhancing average MDCT density of – 130 HU (fat).
The above-described features are those of a left-sided fat containing lesion most consistent with internal angular dermoid cyst. Dermoid cysts represent the most common congenital lesion of the orbit. The most common location is at the frontozygomatic suture (80%) followed by the nasal aspect of upper orbit at the frontoethmoidal suture. Orbital dermoid cysts could be diagnosed if the fatty components are found within it. Some dermoid cysts appear with fluid levels at the superior component of the lesion is a transparent field of fat and the lower component is relatively dense. It is called the "fat-floating" sign.